WASHINGTON (AP) - Faced with serious safety questions, the maker of the experimental impotence drug Uprima withdrew its application for government approval Friday, leaving its fate in limbo.

Uprima once was expected to become the first real competitor for the famous blue impotence pill Viagra, after advisers to the Food and Drug Administration recommended in April that Uprima be sold.

But those same advisers warned the drug can cause a serious side effect: One in 30 men who tested the optimal dose fainted or suffered severe low blood pressure. One man crashed his car; another fell and fractured his skull.

Several of the FDA's advisers bluntly warned that if Uprima is ever sold, this side effect will kill some people.

Today was the FDA's deadline to decide Uprima's fate: let it sell with strong warnings on how men can minimize the risk, like the advisers suggested; reject it; or require more safety studies.

But before the government formally rendered a decision, manufacturer TAP Pharmaceuticals announced it was withdrawing Uprima's FDA application, a sign the company expected rejection.

"We knew they had questions," acknowledged TAP spokeswoman Kim Modory.

TAP stressed, however, that it believes Uprima is effective and thus it plans to again seek FDA approval after new data from clinical trials becomes available later this summer.

"TAP is very committed to patient care, and it is our hope that by taking the extra time to submit additional data, TAP will be able to provide a treatment with an even stronger product profile," TAP president Thomas Watkins said in a statement.

But consumer advocate Dr. Sidney Wolfe of Public Citizen called it "inconceivable" that additional study results would disprove Uprima's danger.

"If this company is smart it will permanently kill this drug," he said. "This drug is just unacceptably dangerous and barely effective."

Viagra became a huge seller when, in 1998, it became the only oral treatment for the impotence believed to afflict some 30 million men. But many men aren't helped by Viagra; hence interest in Uprima.

Viagra has killed some men. Its big risk is a deadly interaction when taken by men using nitrate-containing heart medicine; others had heart attacks.

TAP, a joint venture between Abbott Laboratories and Takeda Pharmaceuticals, said in studies of 3,000 Uprima patients, no one died or had heart attacks. Data recently submitted to FDA shows 4.4 percent of Uprima users fainted, Modory said.

Viagra increases blood flow in the penis, while Uprima, in contrast, increases levels of a brain chemical thought important for causing erections.

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